Device and method for evaluating a useful signal originating from a proximity sensor

ABSTRACT

The invention relates to a device and method for evaluating a useful signal U(t) originating from a proximity sensor. The device comprises a first recognition means ( 17 ) which changes the switching state thereof when the value (U 1 (t)) of a first signal produced from the useful signal exceeds a first limit value that characterizes the proximity of an object. In addition, a second recognition means ( 34 ) is provided which changes the switching state thereof from a first to a second state when the value (U(t)) of the useful signal exceeds a second limit value that characterizes the removal of an object. A decision means ( 32 ), which is connected to the first recognition means ( 17 ) and to the second recognition means ( 34 ), changes its switching state when the first recognition means ( 17 ) changes the switching state thereof from its first to a second switching state, and the second recognition means does not change the switching state thereof during a predetermined first time span (Δt 1 ) after the switching state of the first recognition means is changed.

DESCRIPTION FIELD OF THE INVENTION

[0001] The invention relates to a device as well as a method for evaluating a useful signal originating from a proximity sensor, more especially from an opto-electronic proximity sensor in accordance with the main preamble of claims 1 or 11.

BACKGROUND TO THE INVENTION

[0002] In almost all electric or electronic devices, manual operation is effected by switches. These switches are almost always designed mechanically, two metal parts being brought into contact or respectively out of contact in order to close or respectively to open a circuit. However, this mechanical design has the disadvantage, amongst others, that it has mechanical wearing parts and consequently only has a limited service life and is fundamentally water-sensitive, such that, where required, a costly casing is necessary.

[0003] Optical switches are already known; however up to now they have been extremely lavish and, consequently, expensive and do not yet have the required standard as regards operational reliability. However, in principle, optical switches have advantages, as they manage, generally speaking, without any moving mechanical parts and the switching process can be triggered by mere tapping or by contacting a control surface or by simply through approximation to a sensor.

[0004] PATENT ABSTRACTS OF JAPAN vol. 007, No. 266 (P-239) Nov. 26, 1983 and JP 58 147670 make known an opto-electronic detection circuit, where for elimination of the detection sensitivity, a single signal is taken apart and a portion of the signal is supplied in a time-delayed manner to a comparator. The DC signal is then differentiated. In this case it is not a question of the acquisition and above all not of the evaluation of a typical signal curve for a switching displacement.

[0005] Other patent applications deal with hysteresis problems in order to recognize signals clearly above all against background signals. A circuit for eliminating hysteresis problems is described in EP 0 518 648 and also in PATENT ABSTRACTS OF JAPAN vol.13, no. 330 (E793), Jul. 25, 1989 and JP 01 093915. However, in these cases, the signal curves, which are generated when an object is displaced, are not tested for a curve which is significant to a switching movement.

[0006] U.S. Pat. No. 5,592,033 also deals with hysteresis problems for connecting a second voltage source. A relatively long time delay is used, in this case, to suppress short-term changes in ambient light (column 6, lines 60-65). The two changes in state of one single signal are observed.

[0007] In U.S. Pat. No. 4,381,466 A and the associated publication FUKUYAMA, T.: “Ways to prevent malfunction in photoelectric switches”, JEE JOURNAL OF ELECTRIC ENGINEERING, JP, DEMPA PUBLICATIONS INC., Tokyo, Bd.21, No. 205, 1984, Pages 59-63, signals, which are determined by an opto-electronic detection circuit, are cleaned of interference by a shift register. However, this deprives this circuit of the possibilities of acquiring dynamic changes, as do occur with switching processes. These are not concerned, however, with the recognition of signal curves which are typical of the approximation and removal of an object.

[0008] Furthermore, so-called proximity sensors or also rain sensors are known in the technology, by means of which the displacement of an object onto a surface or the contacting or wetting of a surface can be detected, devices being known in these cases which output a signal containing data regarding the direction of displacement and the speed of displacement of the object. Such a device is known, for example, in WO 95/01561.

OBJECT OF THE INVENTION

[0009] It is the object of the invention to make available a device or respectively a method for evaluating a useful signal originating from a proximity sensor, by means of which signal an optical switch can be operated. Optical switch in this case means that through the intermediary of a defined displacement, for example of a finger, a defined switching process is triggered, that is to say more especially the interrupting or respectively closing of an electric circuit.

[0010] This object is achieved with a device with the characteristics of claim 1 or through a method with the characteristics of claim 11. Advantageous exemplified embodiments are produced from the sub claims

ILLUSTRATION OF THE INVENTION

[0011] To better represent the invention, the arrangement described in WO 95/01561 is initially represented in brief, the disclosure content of which is hereby expressly also made the object of the present application. However, it must be stressed that the present invention is not restricted to operating only with the arrangement described in this case, but can operate whenever there is a useful signal, which contains speed data and direction data on a moving object. This speed data, as a rule, is only available in one dimension and this is also sufficient for the operation of the device according to the invention, amplifier 4. The synchronous demodulator 5 divides the signal of the light sources 1 and 3, which is common to the signal path of the light receiver 2, of the high-pass filter 132 and of the amplifier 4, back into two separate paths. The signal sections cut out by the synchronous demodulator 5, are cleaned in the low pass filters 6 and 7 of nuisance spectral regions and are supplied to the comparator 9. In the case represented, the comparator 9 comprises a simple operation amplifier. The difference values corresponding to the light emitters are at the outputs of the respective low pass filters 6 and 7. In the correspondingly tuned state, that is two times the value zero. These two signals are supplied to the comparator 9. The voltage value U(t), the useful signal, is at the output of this comparator. This signal is also supplied to the signal centering level 11 via a low pass filter 10.

[0012] The output of the signal centering level 11 is connected to a regulator 12, which regulates the signal voltage for the light-emitting diode 3. The achievement of this arrangement is that the useful signal changes where there is a change in the reflection of the light beam emitted by the light-emitting diode 1, however is always continuously returned to zero value. The time constant for this resetting is determined in the exemplified embodiment by the low-pass filter 10.

[0013] It is now the object of the invention to use the useful signal U(t) to the effect that a defined switching process is triggered by a defined displacement of an object. In the present example, the tapping of a finger, of a hand or of another part of the body of the user onto a sensor-active region S on the glass plate 31 is to be detected and a switching process consequently triggered. However, other applications are conceivable, where the displacement of a mechanical element, for example a so-called “jumping jack”, is to be detected.

[0014] The invention is now explained in more detail by way of an exemplified embodiment. In which:

[0015]FIG. 1a is a switching arrangement for the evaluating according to the invention of a useful signal,

[0016]FIG. 1b is a complete arrangement of an optical switch,

[0017]FIG. 2 is the curve of the useful signal U(t) when the sensor-active region is tapped, p FIG. 3.1 is the curve of the measuring signal when the sensor-active region is wiped over,

[0018]FIG. 3.2 is the curve of the useful signal, if, for example, a cloth is moved rapidly to and fro on the glass plate,

[0019]FIG. 4a is the curve of the useful signal U(t) when the sensor-active region is tapped,

[0020]FIG. 4b is the curve of the differentiated displacement signal U₁(t) when the sensor-active region is tapped,

[0021]FIG. 5a is the curve of the measuring signal when the sensor-active region is wiped over,

[0022]FIG. 5b is the curve of the output signal of the first threshold value switch in the situation represented in FIG. 5a,

[0023]FIG. 6 is the signal curves of U₂₀(t) and U_(R)(t), as well as the stored value U_(R)(t₀),

[0024]FIG. 7 is a proximity sensor according to the state of the art,

[0025]FIGS. 8, 9 are possible modifications to the proximity sensor in FIG. 7

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0026] The invention is now described in more detail as an example with reference to the enclosed drawings. However, the exemplified embodiments are only examples, which are not to restrict the inventive concept to one certain arrangement.

[0027] The useful signal U(t) output by the sensor device described above is represented in various situations in FIGS. 2, 3.1 and 3.2. FIG. 2 records the useful signal U(t) when the sensor-active region S is tapped. A switching process is to be triggered by this type of signal. Useful signal curves are recorded in FIG. 3.1 or respectively FIG. 3.2 as occur when the sensor-active region S is wiped over once or respectively when it is wiped over to and fro. These types of signal curves are not to trigger switching processes. This goal is achieved with this embodiment as follows (FIG. 1a):

[0028] The useful signal U(t) is supplied to the high-pass filter 16, which works here as differentiator, such that the value U₁(t) of the differentiated displacement signal is situated at the output of the high-pass filter. Where an object, for example a finger, is displaced onto the sensor-active surface of the glass plate 31, the value U(t) of the useful signal increases slowly analogous to the displacement and stops suddenly when the finger is braked on the glass plate 31, see FIGS. 2 and 4a. If the finger remains and does not move, the value U(t) of the useful signal is regulated slowly back to U₀. The sudden change in value of the useful signal results at the output of the high-pass filter 16 in a jump in the value of the displacement signal U₁(t), see FIG. 4b. This is detected by the threshold value switch 17 when a predetermined negative value U_(G1) is exceeded and the output of the first threshold switch 17, which is connected to the set-input of the first flip-flop 32, is set to active and consequently the first flip-flop 32 is set. The cut-off frequency of the high-pass filter 16 is selected such that a tapping at moderate speed still results in an easily detectable signal. The cut-off frequency could, for example, be in the range of 100 Hertz.

[0029] A signal generated from the useful signal is used therefore in this case, that is to say the displacement signal obtained through differentiation, and this triggers a first process when its value U₁(t) exceeds a certain limit value U_(G1). Switching arrangements and cases of application are also conceivable, however, where the useful signal is used directly and triggers a process—change in flip-flop state in this case—, when the value U(t) of the useful signal exceeds a certain value or falls below a certain value.

[0030] Every displacement, which is quick enough and covers the first sensor-active region, triggers this process, i.e. the output of the first flip-flop 32 is initially set to active. A wiping movement or similar is also sufficient to do this, but it is not, however, to be recognized as a deliberate switching process (see FIGS. 3.1 and 3.2). This is why the useful signal is supplied to a second threshold value switch 34, which becomes active when the value U(t) of the useful signal falls below a certain second threshold value U_(G2). The fact that the removing of an object (removal of a finger) results in a dropping of U(t) into the negative range (FIG. 3.1) is made use of here. Where the second threshold value U_(G2) of the second threshold value switch 34 is exceeded, its output voltage U₃₄ is set to active (see FIG. 5).

[0031] The output of the threshold value switch 34 is connected to the reset-input of the flip-flop 32, such that where there is a wiping movement or similar, which has set the flip-flop 32 to active, it is reset to zero a short time later. This means that the output of the flip-flop 32 is reset back to zero. The output signal of the flip-flop 32 is then supplied to the time detection circuit 33. This circuit is set up such that its output is only set to active if the flip-flop 32 has been active longer than a predetermined time Δt₁, for example 100 ms. This predetermined first time slot Δt₁ corresponds substantially to the normal minimum dwell time of a finger, a hand or another part of the body when tapping a switch, which is configured as an electric switching element.

[0032] The output of the time detection circuit 33 is connected to the set-input of the second flip-flop 18. Where there is a deliberate tapping of the sensor-active surface, the out-put of the second flip-flop 18 is consequently set to active, as in this case the time between setting the first flip-flop 32 and resetting this flip-flop is greater than Δt₁, in other words: The finger remains longer than Δt₁ on the sensor-active surface 26. However, where there are movements, which are not to trigger any switching process —for example wiping over with a cloth—, the time between setting and resetting the first flip-flop 32 is smaller than Δt₁, such that these movements do not result consequently in the second flip-flop 18 being set. Therefore, by tapping the sensor-active surface, the state of the second flip-flop 18 is changed in a controlled manner. The output of the flip-flop 18 can also be connected to a switch 23, for example a relay.

[0033] In many application cases it is desirable for the second flip-flop 18, which is set through the tapping of the sensor-active surface 26, to be reset again by targeted removal of the finger. This then produces the function of a key. However, it is advantageous when the clearing of the flip-flop 18 is not achieved until the finger has been removed a few millimeters from the glass plate, so as to prevent the flip-flop from being cleared inadvertently through a minimal displacement. This problem is solved as follows in the exemplified embodiment represented in this case:

[0034] The instantaneous value of the control signal U_(R)(t), which is situated at the output of the operation amplifier 11, is scanned and stored at a moment at which the approximating object is still situated just in front of the operator interface. To achieve this, this signal is supplied to the delay circuit 20. The voltage value U₂₀, which is situated at the output of the delay circuit 20, is stored in the memory 21 at the moment t₀ at which there is a signal situated at the output of the first threshold value switch 17, that is to say at the moment at which the first threshold value switch 17 has recognized the moment of the tapping. The value U_(R)(t₀), stored in this way, is supplied to a first input of the comparator 22. The control signal with the value U_(R)(t) is located at the second input of the comparator. As long as the value of the control signal is above the value at the output of the memory 21, the comparator circuit 22 does not supply an output signal. However, if the value of the control signal at moment t₁ falls below the stored value, the output of the comparator is set to active. The signals U₂₀, U_(R)(t) and U_(R)(t₀) are represented in FIG. 6. The second flip-flop 18 is reset with this signal.

[0035] The principle of the invention is fundamentally based on evaluating a useful signal originating from a proximity sensor, more especially from an opto-electronic proximity sensor, the value U(t) of which useful signal changes when an object is moved nearer to the proximity sensor and when it is removed away from the proximity sensor and the direction and amount of this change are characteristic of the direction and speed and/or distance of the object.

[0036] To this end, a first recognizing means 17 changes its switching state from a first to a second state when the value U(t) of the useful signal or a value U₁(t) of a first signal generated from the useful signal exceeds or falls below a first limit value which is characteristic of the approximation of an object. A second recognizing means 34 changes its switching state from a first to a second state when the value U(t) of the useful signal or the value of a second signal generated from this useful signal exceeds or falls below a second limit value which is characteristic of the removal of an object. Connected to the recognizing means 17, 34 is a deciding means 32, which changes its output state from a first to a second state when the first recognizing means 17 changes its switching state from its first to its second switching state and the second recognizing means does not change its switching state within a predetermined first time slot Δt1 once the switching state of the first recognizing means has been changed.

[0037] The principle can include more elements in a further development. For example, in this way a third recognizing means resets the output state of the deciding means from the second back to the first output state when the value U(t) of the useful signal or the value U₃(t) of a third signal generated from this useful signal falls below or exceeds a third limit value which is characteristic of the removal of the object. The third limit value is preferably generated from the time curve of the useful signal or of a signal generated by the useful signal. This third limit value corresponds to the value U(t) of the useful signal or of a signal generated by the useful signal at a moment, which lies a certain predetermined time slot before the moment (t₀) of the changing of the state of the first recognizing means (17). This can be achieved by a fixed part factor or by a time-delaying of the control signal U_(R)(t), so as to be independent of appearances of wear and tear, for example, on the surface of the switch. Useful signal, first signal and second signal are preferably analogue voltage signals.

[0038] In the deciding means the first recognizing means 17 sets a first flip-flop 32 and the second recognizing means 34 resets the first flip-flop 32. A time detection circuit 33, which is connected to the output of the first flip-flop 17, is set to active when the out-put of the first flip-flop 32 has been set to active for a time slot which is longer than the predetermined time slot Δt₁. The output of the time detection circuit 33 sets a second flip-flop 18.

[0039] This can consequently be used to form an opto-electronic switch, which is equipped with at least one light-emitting transmitting element and at least one receiving element. The receiving element outputs its signals, the value of which depends on the amount of light received, to an evaluation unit, in which at least one switching element changes its switching state when the value of the first signal, or the value of another signal derived from this signal, exceeds or falls below predetermined limit values. Transmitting and receiving elements can be disposed in such a manner that the light coming from the transmitting element is diffused or reflected by objects, which are located within a certain region, or by a displaceable element, which is at a predetermined spacing from the receiving element and the transmitting element, such that at least one portion of this diffused or reflected light reaches the receiving element. Consequently, the change in the amount of reflected or diffused light, which is received by the receiving element, caused by a displacement of the object or by a displacement of the displaceable element, causes a change in state of the switching element if the displacement is inside the limits of a predetermined displacement pattern.

[0040] This displacement pattern is preferably a tapping of a defined region by finger, hand or another part of the body. For example, a defined region on a glass or plexiglass pane or on a photoconductor, which is connected to the transmitting element and/or receiving element, can be tapped.

[0041] The addressed displaceable element can, for example, be a snap-type spring, as is sometimes used in conventional switches. The recognizing means either recognizes just the displacement pattern of this snap-type spring on its own or in addition to the approximation of the object. For example, the snap-type spring can be situated on the proximity sensor so as to show the user the switching effect in a tactile manner, however just the displacement of the displaceable element on its own can also be detected and evaluated. The snap-type spring is displaceable against a restoring force and can, for example, overcome a dead point when moving against the restoring force.

[0042] It is obvious that this description can be subject to the most varied modifications, changes and adaptations, which range in the region of equivalents to the attached claims.

[0043] This displacement pattern is preferably a tapping of a defined region by finger, hand or another part of the body. For example, a defined region on a glass or plexiglass pane or on a photoconductor, which is connected to the transmitting element and/or receiving element, can be tapped.

[0044] The addressed displaceable element can, for example, be a snap-type spring, as is sometimes used in conventional switches. The recognizing means either recognizes just the displacement pattern of this snap-type spring on its own or in addition to the approximation of the object. For example, the snap-type spring can be situated on the proximity sensor so as to show the user the switching effect in a tactile manner, however just the displacement of the displaceable element on its own can also be detected and evaluated. The snap-type spring is displaceable against a restoring force and can, for example, overcome a dead point when moving against the restoring force. 

1. Device for evaluating a useful signal originating from a proximity sensor, more especially from an opto-electronic proximity sensor, wherein the value (U(t)) of the useful signal changes with the approximation of an object to the proximity sensor and with the removal of an object from the proximity sensor and the direction and amount of this change are characteristic of the direction and speed and/or distance of the object, having a first recognizing means (17), which changes its switching state from a first to a second state when a first value (U(t)) of the useful signal or a first value (U₁(t)) of a first signal generated from this useful signal, exceeds or falls below a first limit value, which is characteristic of the approximation of an object, a second recognizing means (34), which changes its switching state when a second value (U(t)), (U₁(t)) exceeds or falls below a second limit value, which is characteristic of the approximation of an object, a deciding means (32) which is connected to the first and second recognizing means (17, 34) and changes its output state from a first into a second switching state when the first recognizing means (17) changes its switching state from its first to its second state and when the second recognizing means (34) does not change its switching state, characterized in that the second recognizing means (32) changes its switching state when the object is removed, the deciding means (32) maintains its second state when in addition the second recognizing means (34) does not change its switching state within a predetermined first time slot (Δt₁) once the switching state of the first recognizing means has been changed, and the output of a time detection circuit (33), which is connected to the output of the first deciding means (32), is set to active when the output of the first deciding means (32) has been set to active for a time slot which is longer than the predetermined time slot (Δt₁) and a second deciding means (18) is connected to the output of the time detection circuit (33).
 2. Device according to claim 1, characterized in that a third recognizing means (20, 21, 22) is provided, which resets the output state of the second deciding means (18) from the second back to the first output state when the value (U(t)) of the useful signal or the value (U_(R)(t)) of a third signal generated from this useful signal falls below or exceeds a third limit value, which is characteristic of the removal of the object.
 3. Device according to claim 2, characterized in that the third limit value is generated from the time curve of the useful signal or of a signal generated from the useful signal.
 4. Device according to claim 3, characterized in that the third limit value corresponds to the value (U(t)) of the useful signal or of a signal generated from the useful signal, at a moment which lies a certain predetermined time slot before the moment (t0) of the changing of the state of the first recognizing means (17).
 5. Device according to one of the preceding claims, characterized in that the deciding means (32) is connected downstream of the recognizing means (17, 34) and an electric switching element is connected directly downstream of this latter such that the change in the switching state of the deciding means (32) results in the switching of the switching element (23).
 6. Device according to one of the preceding claims, characterized in that the useful signal, the first signal and the second signal are analogue voltage signals.
 7. Device according to claim 6, characterized in that the first recognizing means consists of a high-pass filter (16), at the input of which is the useful signal (U(t)), and a first threshold value switch (17), which is connected downstream.
 8. Device according to claim 6 or 7, characterized in that the second recognizing means is a second threshold value switch (34), at the input of which is the useful signal (U(t)).
 9. Device according to claims 6 to 8, characterized in that the deciding means has the following component parts: a first flip-flop (32), the set input of which is connected to the output of the first threshold value switch (17) and the reset input of which is connected to the out-put of the second threshold value switch (34), a time detection circuit (33) connected to the output of the first flip-flop (32), the output of which time detection circuit is set to active when the output of the first flip-flop (32) has been set to active for a time slot which is longer than the predetermined time slot (Δt₁) and a second flip-flop (18), the set input of which is connected to the output of the time detection circuit (33).
 10. Device according to one of claims 1 to 9, characterized in that the approaching object is at least one finger, one hand or another body part of a user, and in that the predetermined first time slot (Δt₁) corresponds to the normal dwell time of the finger, the hand or the other body part when tapping a switch which is configured as an electric switching element.
 11. Method for evaluating a useful signal originating from a proximity sensor, more especially from an opto-electronic proximity sensor, using a device in accordance with one of the preceding claims, wherein a value (U(t)) of the useful signal or a value (U1 (t)) of a signal generated from this useful signal changes when an object approaches the proximity sensor and when an object is removed from the proximity sensor and the direction and amount of this change are characteristic of the direction and speed and/or distance of the object, having the steps: Recognition of the approaching of the object and switching of a first recognizing means (17) when the first value (U(t)), (U₁(t)) of a first signal exceeds or falls below a first limit value which is characteristic of the approaching of an object, Recognition of the approaching of the object and switching of a second recognizing means (34) when the second value (U(t)), (U₁(t)) exceeds or falls below a second limit value characteristic of the approaching of the object and Change the output state of a deciding means (32) which is connected to the recognizing means (17, 34) when the first recognizing means (17) changes its state and when the second recognizing means (34) does not change its state, characterized by the further steps Recognition of the removal of the object by switching a second recognizing means (34), Maintaining the second state of the deciding means (32) when in addition the second recognizing means does not change its switching state within a predetermined first time slot (Δt₁) once the switching state of the first recognizing means has been changed, Setting to active the output of a time detection circuit (33), which is connected to the output of the first deciding means (32), when the output of the first deciding means (32) has been set to active for a time slot which is longer than the predetermined time slot (Δt₁) and Connecting a second deciding means (18) to the output of the time detection circuit (33).
 12. Method according to claim 11, characterized in that a third recognizing means (20, 21, 22) resets the output state of the second deciding means (18) from the second state back to the first output state when the value (U(t)) of the useful signal or the value (UR(t)) of a third signal generated from this useful signal falls below or exceeds a third limit value which is characteristic of the removal of the object.
 13. Method according to claim 12, characterized in that the third limit value is generated from the time curve of the useful signal or of a signal generated from the useful signal, which lies preferably a certain predetermined time slot before the moment (t₀) of the changing of the state of the first recognizing means (17).
 14. Method according to one of claims 11 to 13, characterized in that the change in state of the second deciding means (18) switches an electric switching element (23).
 15. Method according to one of claims 11 to 14, characterized in that in the first deciding means the first recognizing means (17) sets a first flip-flop (32) and the second recognizing means (34) resets the first flip-flop (32), and in that a time detection circuit (33), which is connected to the output of the first flip-flop (32), is set to active when the output of the first flip-flop (32) has been set to active for a time slot which is longer than the predetermined time slot (Δt₁), and in that the output of the time detection circuit (33) sets a second flip-flop (18) 